The present invention relates to novel catalysts for the polymerization of epoxides, to the preparation of such catalysts as well as to process for the polymerization of epoxides using novel catalysts according to the present invention.
The polymerization of epoxides such as propylene oxide or mixtures of propylene oxide and ethylene oxide using water and/or alcohols as initiators is of great industrial importance since the resulting polyether alcohols or polyether polyols are very versatile compounds which can be used as such or as intermediates in the manufacture of various products such as (flexible) polyurethanes, detergents, oil additives and brake fluids.
The polymerization of epoxides is normally carried out under basic conditions, i.e. by using potassium hydroxide or sodium hydroxide as a catalyst. Although products (polyether polyols or polyether alcohols) of good quality can be obtained, the use of these inorganic bases limits the capacity of the process since a long batch time is required to warrent good quality products. Shortening of the batch time is not impossible but it has the intrinsic disadvantage that the selectivity of the process is decreased substantially, which seriously affects the product properties.
Therefore, alternative catalytic systems allowing in principle a shorter batch time have already been proposed in the art. Reference is made in this respect to double metal cyanide complexes such as are disclosed in British Patent Specification No. 1,149,726 (for instance zinc hexacyanometallate complexes also containing zinc chloride, water and an organic ligand) and in East German Patent Specification No. 148,957 (specificcally metal hexacyano-iridium complexes also containing zinc chloride, water and an ether). The preparation of such double metal cyanide complexes is rather complicated and tedious. Moreover, the preparation will be normally carried out via the intermediate free acid which could cause great problems in upscaling, not only from an equipment point of view (ion-exchange columns are required) but also from a safety point of view (potential release of hydrogen cyanide). In particular, filtration and/or centrifugation problems already severe in small-scale operations would make a full-scale operation unecomonical. It is therefore of great importance to develop a catalytic system which can be prepared without the preparative drawbacks referred to hereinbefore whilst maintaining the intrinsic advantages of the double metal cyanide-type complexes.
A novel class of double metal cyanide-type compounds has now been found which surprisingly can be prepared without any of the major handling problems referred to hereinbefore. This class of novel double metal cyanide-type compounds further appears to be very stable, both as such and in admixture with the appropriate initiator, which makes these compounds also attractive from a storage/usage point of view.